Congestion control in a wireless data network

ABSTRACT

Techniques for congestion control are disclosed. In an embodiment, a base station allocates a shared resource using a combination of zero or more individual grants and zero or more common grants, and generates a multi-valued busy signal in response to loading conditions that exceed a pre-determined level. In another embodiment, a subset of transmitting mobile stations reduce their transmission rate in response to a multi-valued busy signal. The subset may include autonomous transmission, commonly granted transmission, individually granted transmission, or any combination thereof. In various embodiments, rate adjustment may be probabilistic or deterministic. In an embodiment, a rate table is deployed, and a mobile station decreases or increases the transmission rate from one rate in the table to a lower or higher rate in the table, respectively, in response to the busy signal. Various other aspects provide efficient congestion control, avoiding excessive interference and increasing capacity.

CLAIM OF PRIORITY UNDER 35 U.S.C. SECTION 119

The present application is a continuation of U.S. application Ser. No.10/646,242, filed Aug. 22, 2003, entitled “CONGESTION CONTROL IN AWIRELESS DATA NETWORK,” which claims priority to provisional applicationSer. No. 60/448,269, entitled “REVERSE LINK DATA COMMUNICATION,” filedon Feb. 18, 2003; U.S. provisional application Ser. No. 60/452,790,entitled “METHOD AND APPARATUS FOR A REVERSE LINK COMMUNICATION IN ACOMMUNICATION SYSTEM,” filed on Mar. 6, 2003; U.S. provisionalapplication, and Ser. No. 60/470,770, entitled “OUTER-LOOP POWER CONTROLFOR REL. D,” filed on May 14, 2003.

FIELD

The present invention relates generally to wireless communications, andmore specifically to a novel and improved method and apparatus forcongestion control in a wireless data network.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustypes of communication such as voice and data. These systems may bebased on code division multiple access (CDMA), time division multipleaccess (TDMA), or some other multiple access techniques. A CDMA systemprovides certain advantages over other types of systems, includingincreased system capacity.

A CDMA system may be designed to support one or more CDMA standards suchas (1) the “TIA/EIA-95-B Mobile Station-Base Station CompatibilityStandard for Dual-Mode Wideband Spread Spectrum Cellular System” (theIS-95 standard), (2) the standard offered by a consortium named “3rdGeneration Partnership Project” (3GPP) and embodied in a set ofdocuments including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offeredby a consortium named “3rd Generation Partnership Project 2” (3GPP2) andembodied in “TR-45.5 Physical Layer Standard for cdma2000 SpreadSpectrum Systems” (the IS-2000 standard), and (4) some other standards.

In the above named standards, the available spectrum is sharedsimultaneously among a number of users, and techniques such as powercontrol and soft handoff are employed to maintain sufficient quality tosupport delay-sensitive services, such as voice. Data services are alsoavailable. More recently, systems have been proposed that enhance thecapacity for data services by using higher order modulation, very fastfeedback of Carrier to Interference ratio (C/I) from the mobile station,very fast scheduling, and scheduling for services that have more relaxeddelay requirements. An example of such a data-only communication systemusing these techniques is the high data rate (HDR) system that conformsto the TIA/EIA/IS-856 standard (the IS-856 standard).

In contrast to the other above named standards, an IS-856 system usesthe entire spectrum available in each cell to transmit data to a singleuser at one time, selected based on link quality. In so doing, thesystem spends a greater percentage of time sending data at higher rateswhen the channel is good, and thereby reduces committing resources tosupport transmission at inefficient rates. The net effect is higher datacapacity, higher peak data rates, and higher average system throughput.

Systems can incorporate support for delay-sensitive data, such as voicechannels or data channels supported in the IS-2000 standard, along withsupport for packet data services such as those described in the IS-856standard. The cdma2000® Revision C of the IS-2000 standard (includingC.S0001.C through C.S0006.C) is such a system, and is hereinafterreferred to as the 1xEV-DV system. In the rest of the document, we'llrefer to release 0, A, and B of the cdma2000® standard as cdma2000,while revision C and upwards will be referred to as 1xEV-DV systems.

An example 1xEV-DV system includes a reverse link control mechanism forallocating the shared reverse link resource for transmission by aplurality of mobile stations. A mobile station may make a request to aserving base station for transmission permission with a maximum ratesupportable by the mobile station. Alternatively, a mobile station isallowed to transmit autonomously, without making a request, at a rate upto a determined autonomous maximum rate. The serving base stationanticipates an expected amount of autonomous transmission on the reverselink, reviews any requests made by mobile stations, and allocates theshared resource accordingly. The base station may elect to make one ormore individual grants to requesting mobile stations, and includes themaximum rate for those grants. The remaining requesting mobile stationsmay be issued permission to transmit according to a common grant, withan associated maximum transmission rate. Thus, the serving base stationattempts to maximize utilization of the shared resource with acombination of individual and common grants, in the presence ofautonomous transmission by other mobile stations. Various techniques maybe used to allow mobile stations to continue transmitting according to adetermined allocation and the associated grants, with a minimum amountof signaling required.

From time to time, the amount of loading on the reverse link may exceedthe amount predicted by the serving base station. Various factors maylead to this system over-utilization, an example of which is theuncertainty in the actual number of autonomous transmissions that maytranspire. Overall throughput, and thus effective capacity of thesystem, may deteriorate when the system becomes congested. For example,a resultant increase in error rate may result in loss of successful datatransmission, and subsequent retransmission will use additional capacityon the shared resource. While the allocation and granting procedure justdescribed may be used to alleviate overloading on the system, there islatency associated with the messaging required. Capacity and throughputmay be adversely affected during this time. It is desirable to be ableto reduce the system loading quickly to minimize these adverse effects.

Furthermore, additional messaging also uses system capacity. In somecircumstances, the system overload is a temporal condition, after which,the previous allocation and associated grants will be appropriate forthe desired system load. It is desirable for the various mobile stationsto return to the prescribed allocation while minimizing messagingoverhead. There is therefore a need in the art for congestion control toreduce system loading efficiently.

SUMMARY

Embodiments disclosed herein address the need for congestion control. Inone embodiment, a base station allocates a shared resource using acombination of zero or more individual grants and zero or more commongrants, and generates a busy signal in response to loading conditionsthat exceed a pre-determined level. In another embodiment, a subset oftransmitting mobile stations reduce their transmission rate in responseto a busy signal. In one embodiment, autonomously transmitting mobilestations adjust transmission rates in response to a busy signal. Inanother embodiment, commonly granted mobile stations adjust transmissionrates in response to a busy signal. In yet another embodiment,individually granted mobile stations adjust transmission rates inresponse to a busy signal. In various embodiments, rate adjustment maybe probabilistic or deterministic. In one embodiment, a rate table isdeployed, and a mobile station decreases or increases the transmissionrate from one rate in the table to a lower or higher rate in the table,respectively, in response to the busy signal. Various other aspects arealso presented. These aspects have the benefit of providing efficientutilization of the reverse link capacity, accommodating varyingrequirements such as low-latency, high throughput or differing qualityof service, and reducing forward and reverse link overhead for providingthese benefits, thus avoiding excessive interference and increasingcapacity.

The invention provides methods and system elements that implementvarious aspects, embodiments, and features of the invention, asdescribed in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a general block diagram of a wireless communication systemcapable of supporting a number of users;

FIG. 2 depicts an example mobile station and base station configured ina system adapted for data communication;

FIG. 3 is a block diagram of a wireless communication device, such as amobile station or base station;

FIG. 4 depicts an exemplary embodiment of data and control signals forreverse link data communication;

FIG. 5 contrasts the R-ESCH power level with and without fast control;

FIG. 6 depicts a method of congestion control that may be performed in abase station;

FIG. 7 depicts a generalized method of congestion control performed at amobile station;

FIG. 8 depicts a method of congestion control with set rate limits;

FIG. 9 depicts a method of congestion control using a tri-valued busysignal; and

FIG. 10 depicts an embodiment of a rate table that may be deployed withany congestion control method.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a wireless communication system 100 that may bedesigned to support one or more CDMA standards and/or designs (e.g., theW-CDMA standard, the IS-95 standard, the cdma2000 standard, the HDRspecification, the 1xEV-DV system). In an alternative embodiment, system100 may additionally support any wireless standard or design other thana CDMA system. In the exemplary embodiment, system 100 is a 1xEV-DVsystem.

For simplicity, system 100 is shown to include three base stations 104in communication with two mobile stations 106. The base station and itscoverage area are often collectively referred to as a “cell”. In IS-95,cdma2000, or 1xEV-DV systems, for example, a cell may include one ormore sectors. In the W-CDMA specification, each sector of a base stationand the sector's coverage area is referred to as a cell. As used herein,the term base station can be used interchangeably with the terms accesspoint or Node B. The term mobile station can be used interchangeablywith the terms user equipment (UE), subscriber unit, subscriber station,access terminal, remote terminal, or other corresponding terms known inthe art. The term mobile station encompasses fixed wirelessapplications.

Depending on the CDMA system being implemented, each mobile station 106may communicate with one (or possibly more) base stations 104 on theforward link at any given moment, and may communicate with one or morebase stations on the reverse link depending on whether or not the mobilestation is in soft handoff. The forward link (i.e., downlink) refers totransmission from the base station to the mobile station, and thereverse link (i.e., uplink) refers to transmission from the mobilestation to the base station.

While the various embodiments described herein are directed to providingreverse-link or forward-link signals for supporting reverse linktransmission, and some may be well suited to the nature of reverse linktransmission, those skilled in the art will understand that mobilestations as well as base stations can be equipped to transmit data asdescribed herein and the aspects of the present invention apply in thosesituations as well. The word “exemplary” is used exclusively herein tomean “serving as an example, instance, or illustration.” Any embodimentdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other embodiments.

1xEV-DV Forward Link Data Transmission and Reverse Link Power Control

A system 100, such as the one described in the 1xEV-DV proposal,generally comprises forward link channels of four classes: overheadchannels, dynamically varying IS-95 and IS-2000 channels, a ForwardPacket Data Channel (F-PDCH), and some spare channels. The overheadchannel assignments vary slowly; for example, they may not change formonths. They are typically changed when there are major networkconfiguration changes. The dynamically varying IS-95 and IS-2000channels are allocated on a per call basis or are used for IS-95, orIS-2000 Release 0 through B packet services. Typically, the availablebase station power remaining after the overhead channels and dynamicallyvarying channels have been assigned is allocated to the F-PDCH forremaining data services. The F-PDCH may be used for data services thatare less sensitive to delay while the IS-2000 channels are used for moredelay-sensitive services.

The F-PDCH, similar to the traffic channel in the IS-856 standard, isused to send data at the highest supportable data rate to one user ineach cell at a time. In IS-856, the entire power of the base station andthe entire space of Walsh functions are available when transmitting datato a mobile station. However, in the proposed 1xEV-DV system, some basestation power and some of the Walsh functions are allocated to overheadchannels and existing IS-95 and cdma2000 services. The data rate that issupportable depends primarily upon the available power and Walsh codesafter the power and Walsh codes for the overhead, IS-95, and IS-2000channels have been assigned. The data transmitted on the F-PDCH isspread using one or more Walsh codes.

In the 1xEV-DV system, the base station generally transmits to onemobile station on the F-PDCH at a time, although many users may be usingpacket services in a cell. (It is also possible to transmit to two usersby scheduling transmissions for the two users, and allocating power andWalsh channels to each user appropriately.) Mobile stations are selectedfor forward link transmission based upon some scheduling algorithm.

In a system similar to IS-856 or 1xEV-DV, scheduling is based in part onchannel quality feedback from the mobile stations being serviced. Forexample, in IS-856, mobile stations estimate the quality of the forwardlink and compute a transmission rate expected to be sustainable for thecurrent conditions. The desired rate from each mobile station istransmitted to the base station. The scheduling algorithm may, forexample, select a mobile station for transmission that supports arelatively higher transmission rate in order to make more efficient useof the shared communication channel. As another example, in a 1xEV-DVsystem, each mobile station transmits a Carrier-to-Interference (C/I)estimate as the channel quality estimate on the Reverse Channel QualityIndicator Channel (R-CQICH). The scheduling algorithm is used todetermine the mobile station selected for transmission, as well as theappropriate rate and transmission format in accordance with the channelquality.

As described above, a wireless communication system 100 may supportmultiple users sharing the communication resource simultaneously, suchas an IS-95 system, may allocate the entire communication resource toone user at time, such as an IS-856 system, or may apportion thecommunication resource to allow both types of access. A 1xEV-DV systemis an example of a system that divides the communication resourcebetween both types of access, and dynamically allocates theapportionment according to user demand. Following is a brief backgroundon how the communication resource can be allocated to accommodatevarious users in both types of access systems. Power control isdescribed for simultaneous access by multiple users, such as IS-95 typechannels. Rate determination and scheduling is discussed for time-sharedaccess by multiple users, such as an IS-856 system or the data-onlyportion of a 1xEV-DV type system (i.e., the F-PDCH).

Capacity in a system such as an IS-95 CDMA system is determined in partby interference generated in transmitting signals to and from varioususers within the system. A feature of a typical CDMA system is to encodeand modulate signals for transmission to or from a mobile station suchthat the signals are seen as interference by other mobile stations. Forexample, on the forward link, the quality of the channel between a basestation and one mobile station is determined in part by other userinterference. To maintain a desired performance level of communicationwith the mobile station, the transmit power dedicated to that mobilestation must be sufficient to overcome the power transmitted to theother mobile stations served by the base station, as well as otherdisturbances and degradation experienced in that channel. Thus, toincrease capacity, it is desirable to transmit the minimum powerrequired to each mobile station served.

In a typical CDMA system, when multiple mobile stations are transmittingto a base station, it is desirable to receive a plurality of mobilestation signals at the base station at a normalized power level. Thus,for example, a reverse link power control system may regulate thetransmit power from each mobile station such that signals from nearbymobile stations do not overpower signals from farther away mobilestations. As with the forward link, keeping the transmit power of eachmobile station at the minimum power level required to maintain thedesired performance level allows for capacity to be optimized, inaddition to other benefits of power savings such as increased talk andstandby times, reduced battery requirements, and the like.

Capacity in a typical CDMA system, such as IS-95, is constrained by,among other things, other-user interference. Other-user interference canbe mitigated through use of power control. The overall performance ofthe system, including capacity, voice quality, data transmission ratesand throughput, is dependent upon stations transmitting at the lowestpower level to sustain the desired level of performance wheneverpossible. To accomplish this, various power control techniques are knownin the art.

One class of techniques includes closed loop power control. For example,closed loop power control may be deployed on the forward link. Suchsystems may employ an inner and outer power control loop in the mobilestation. An outer loop determines a target received power levelaccording to a desired received error rate. For example, a target frameerror rate of 1% may be pre-determined as the desired error rate. Theouter loop may update the target received power level at a relativelyslow rate, such as once per frame or block. In response, the inner loopthen sends up or down power control messages to the base station untilreceived power meets the target. These inner loop power control commandsoccur relatively frequently, so as to quickly adapt the transmittedpower to the level necessary to achieve the desired received signal tonoise and interference ratio for efficient communication. As describedabove, keeping the forward link transmit power for each mobile stationat the lowest level reduces other user interference seen at each mobilestation and allows remaining available transmit power to be reserved forother purposes. In a system such as IS-95, the remaining availabletransmit power can be used to support communication with additionalusers. In a system such as 1xEV-DV, the remaining available transmitpower can be used to support additional users, or to increase thethroughput of the data-only portion of the system.

In a “data-only” system, such as IS-856, or in the “data-only” portionof a system, such as 1xEV-DV, a control loop may be deployed to governthe transmission from the base station to a mobile station in atime-shared manner. For clarity, in the following discussion,transmission to one mobile station at a time may be described. This isto distinguish from a simultaneous access system, an example of which isIS-95, or various channels in a cdma200 or 1xEV-DV system. Two notes arein order at this point.

First, the term “data-only” or “data channel” may be used to distinguisha channel from IS-95 type voice or data channels (i.e. simultaneousaccess channels using power control, as described above) for clarity ofdiscussion only. It will be apparent to those of skill in the art thatdata-only or data channels described herein can be used to transmit dataof any type, including voice (e.g., voice over Internet Protocol, orVOIP). The usefulness of any particular embodiment for a particular typeof data may be determined in part by the throughput requirements,latency requirements, and the like. Those of skill in the art willreadily adapt various embodiments, combining either access type withparameters selected to provide the desired levels of latency,throughput, quality of service, and the like.

Second, a data-only portion of a system, such as that described for1xEV-DV, which is described as time-sharing the communication resource,can be adapted to provide access on the forward link to more than oneuser simultaneously. In examples herein where the communication resourceis described as time-shared to provide communication with one mobilestation or user during a certain period, those of skill in the art willreadily adapt those examples to allow for time-shared transmission to orfrom more than one mobile station or user within that time period.

A typical data communication system may include one or more channels ofvarious types. More specifically, one or more data channels are commonlydeployed. It is also common for one or more control channels to bedeployed, although in-band control signaling can be included on a datachannel. For example, in a 1xEV-DV system, a Forward Packet Data ControlChannel (F-PDCCH) and a Forward Packet Data Channel (F-PDCH) are definedfor transmission of control and data, respectively, on the forward link.

FIG. 2 depicts an example mobile station 106 and base station 104configured in a system 100 adapted for data communication. Base station104 and mobile station 106 are shown communicating on a forward and areverse link. Mobile station 106 receives forward link signals inreceiving subsystem 220. A base station 104 communicating the forwarddata and control channels, detailed below, may be referred to herein asthe serving station for the mobile station 106. An example receivingsubsystem is detailed further below with respect to FIG. 3. ACarrier-to-Interference (C/I) estimate is made for the forward linksignal received from the serving base station in the mobile station 106.A C/I measurement is an example of a channel quality metric used as achannel estimate, and alternate channel quality metrics can be deployedin alternate embodiments. The C/I measurement is delivered totransmission subsystem 210 in the base station 104, an example of whichis detailed further below with respect to FIG. 3.

The transmission subsystem 210 delivers the C/I estimate over thereverse link where it is delivered to the serving base station. Notethat, in a soft handoff situation, well known in the art, the reverselink signals transmitted from a mobile station may be received by one ormore base stations other than the serving base station, referred toherein as non-serving base stations. Receiving subsystem 230, in basestation 104, receives the C/I information from mobile station 106.

Scheduler 240, in base station 104, is used to determine whether and howdata should be transmitted to one or more mobile stations within theserving cell's coverage area. Any type of scheduling algorithm can bedeployed within the scope of the present invention. One example isdisclosed in U.S. patent application Ser. No. 08/798,951, entitled“METHOD AND APPARATUS FOR FORWARD LINK RATE SCHEDULING”, filed Feb. 11,1997, assigned to the assignee of the present invention.

In an example 1xEV-DV embodiment, a mobile station is selected forforward link transmission when the C/I measurement received from thatmobile station indicates that data can be transmitted at a certain rate.It is advantageous, in terms of system capacity, to select a targetmobile station such that the shared communication resource is alwaysutilized at its maximum supportable rate. Thus, the typical targetmobile station selected may be the one with the greatest reported C/I.Other factors may also be incorporated in a scheduling decision. Forexample, minimum quality of service guarantees may have been made tovarious users. It may be that a mobile station, with a relatively lowerreported C/I, is selected for transmission to maintain a minimum datatransfer rate to that user.

In the example 1xEV-DV system, scheduler 240 determines which mobilestation to transmit to, and also the data rate, modulation format, andpower level for that transmission. In an alternate embodiment, such asan IS-856 system, for example, a supportable rate/modulation formatdecision can be made at the mobile station, based on channel qualitymeasured at the mobile station, and the transmit format can betransmitted to the serving base station in lieu of the C/I measurement.Those of skill in the art will recognize myriad combinations ofsupportable rates, modulation formats, power levels, and the like whichcan be deployed within the scope of the present invention. Furthermore,although in various embodiments described herein the scheduling tasksare performed in the base station, in alternate embodiments, some or allof the scheduling process may take place in the mobile station.

Scheduler 240 directs transmission subsystem 250 to transmit to theselected mobile station on the forward link using the selected rate,modulation format, power level, and the like.

In the example embodiment, messages on the control channel, or F-PDCCH,are transmitted along with data on the data channel, or F-PDCH. Thecontrol channel can be used to identify the recipient mobile station ofthe data on the F-PDCH, as well as identifying other communicationparameters useful during the communication session. A mobile stationshould receive and demodulate data from the F-PDCH when the F-PDCCHindicates that mobile station is the target of the transmission. Themobile station responds on the reverse link following the receipt ofsuch data with a message indicating the success or failure of thetransmission. Retransmission techniques, well known in the art, arecommonly deployed in data communication systems.

A mobile station may be in communication with more than one basestation, a condition known as soft handoff. Soft handoff may includemultiple sectors from one base station (or one Base TransceiverSubsystem (BTS)), known as softer handoff, as well as with sectors frommultiple BTSs. Base station sectors in soft handoff are generally storedin a mobile station's Active Set. In a simultaneously sharedcommunication resource system, such as IS-95, IS-2000, or thecorresponding portion of a 1xEV-DV system, the mobile station maycombine forward link signals transmitted from all the sectors in theActive Set. In a data-only system, such as IS-856, or the correspondingportion of a 1xEV-DV system, a mobile station receives a forward linkdata signal from one base station in the Active Set, the serving basestation (determined according to a mobile station selection algorithm,such as those described in the C.S0002.C standard). Other forward linksignals, examples of which are detailed further below, may also bereceived from non-serving base stations.

Reverse link signals from the mobile station may be received at multiplebase stations, and the quality of the reverse link is generallymaintained for the base stations in the active set. It is possible forreverse link signals received at multiple base stations to be combined.In general, soft combining reverse link signals from non-collocated basestations would require significant network communication bandwidth withvery little delay, and so the example systems listed above do notsupport it. In softer handoff, reverse link signals received at multiplesectors in a single BTS can be combined without network signaling. Whileany type of reverse link signal combining may be deployed within thescope of the present invention, in the example systems described above,reverse link power control maintains quality such that reverse linkframes are successfully decoded at one BTS (switching diversity).

In a simultaneously shared communication resource system, such as IS-95,IS-2000, or the corresponding portion of a 1xEV-DV system, each basestation in soft handoff with a mobile station (i.e., in the mobilestation's Active Set) measures the reverse link pilot quality of thatmobile station and sends out a stream of power control commands. InIS-95 or IS-2000 Rev. B, each stream is punctured onto the ForwardFundamental Channel (F-FCH) or the Forward Dedicated Control Channel(F-DCCH), if either is assigned. The stream of commands for a mobilestation is called the Forward Power Control Subchannel (F-PCSCH) forthat mobile station. The mobile station receives the parallel commandstreams from all its Active Set members for each base station (multiplesectors from one BTS, if all in the Active Set of the mobile station,send the same command to that mobile station) and determines if an “up”or “down” command was sent. The mobile station modifies the reverse linktransmit power level accordingly, using the “Or-of-downs” rule, that is,the transmit power level is reduced if any “down” command is received,and increased otherwise.

The transmit power level of the F-PCSCH is typically tied to the levelof the host F-FCH or F-DCCH that carries the subchannel. The host F-FCHor F-DCCH transmit power level at the base station is determined by thefeedback from the mobile station on the Reverse Power Control Subchannel(R-PCSCH), which occupies the last quarter of the Reverse Pilot Channel(R-PICH). Since the F-FCH or the F-DCCH from each base station forms asingle stream of traffic channel frames, the R-PCSCH reports thecombined decoding results of these legs. Erasures of the F-FCH or theF-DCCH determine the required Eb/Nt set point of the outer loop, whichin turn drives the inner loop commands on the R-PCSCH and thus the basestation transmit levels of the F-FCH, F-DCCH, as well as the F-PCSCH onthem.

Due to the potential differences in reverse link path loss to each basestation from a single mobile station in soft handoff, some of the basestations in the Active Set may not receive the R-PCSCH reliably and maynot correctly control the forward link power of the F-FCH, F-DCCH, andthe F-PCSCH. The base stations may need to re-align the transmit levelsamong themselves so that the mobile station retains the spatialdiversity gain of soft handoff. Otherwise, some of the forward link legsmay carry little or no traffic signal energy due to errors in thefeedback from the mobile station.

Since different base stations may need different mobile station transmitpower for the same reverse link set point or reception quality, thepower control commands from different base stations may be different andcannot be soft combined at the MS. When new members are added to theActive Set (i.e. no soft handoff to 1-way soft handoff, or from 1-way to2-way, etc.), the F-PCSCH transmit power is increased relative to itshost F-FCH or F-DCCH.

In a 1xEV-DV system, the Forward Common Power Control Channel (F-CPCCH)transports the reverse link power control commands for mobile stationswhen neither the Forward Fundamental Channel (F-FCH) nor the ForwardDedicated Control Channel (F-DCCH) are assigned. The serving basestation may use the information on the Reverse Channel Quality IndicatorChannel (R-CQICH) to determine the transmit power level of the F-CPCCH.The R-CQICH is principally used in scheduling to determine theappropriate forward link transmission format.

However, when the mobile station is in soft handoff, the R-CQICH onlyreports the forward link pilot quality of the serving base stationsector and therefore cannot be used to directly power control theF-CPCCH from the non-serving base stations. Techniques for this aredisclosed in U.S. Patent Application No. 60/356,929, entitled “Methodand Apparatus for Forward Link Power Control During Soft Handoff in aCommunication System”, filed Feb. 12, 2002, assigned to the assignee ofthe present invention.

Example Base Station and Mobile Station Embodiments

FIG. 3 is a block diagram of a wireless communication device, such asmobile station 106 or base station 104. The blocks depicted in thisexample embodiment will generally be a subset of the components includedin either a base station 104 or mobile station 106. Those of skill inthe art will readily adapt the embodiment shown in FIG. 3 for use in anynumber of base station or mobile station configurations.

Signals are received at antenna 310 and delivered to receiver 320.Receiver 320 performs processing according to one or more wirelesssystem standards, such as the standards listed above. Receiver 320performs various processing such as Radio Frequency (RF) to basebandconversion, amplification, analog to digital conversion, filtering, andthe like. Various techniques for receiving are known in the art.Receiver 320 may be used to measure channel quality of the forward orreverse link, when the device is a mobile station or base station,respectively, although a separate channel quality estimator 335 is shownfor clarity of discussion, detailed below.

Signals from receiver 320 are demodulated in demodulator 325 accordingto one or more communication standards. In an example embodiment, ademodulator capable of demodulating 1xEV-DV signals is deployed. Inalternate embodiments, alternate standards may be supported, andembodiments may support multiple communication formats. Demodulator 330may perform RAKE receiving, equalization, combining, deinterleaving,decoding, and various other functions as required by the format of thereceived signals. Various demodulation techniques are known in the art.In a base station 104, demodulator 325 will demodulate according to thereverse link. In a mobile station 106, demodulator 325 will demodulateaccording to the forward link. Both the data and control channelsdescribed herein are examples of channels that can be received anddemodulated in receiver 320 and demodulator 325. Demodulation of theforward data channel will occur in accordance with signaling on thecontrol channel, as described above.

Message decoder 330 receives demodulated data and extracts signals ormessages directed to the mobile station 106 or base station 104 on theforward or reverse links, respectively. Message decoder 330 decodesvarious messages used in setting up, maintaining and tearing down a call(including voice or data sessions) on a system. Messages may includechannel quality indications, such as C/I measurements, power controlmessages, or control channel messages used for demodulating the forwarddata channel. Various types of control messages may be decoded in eithera base station 104 or mobile station 106 as transmitted on the reverseor forward links, respectively. For example, described below are requestmessages and grant messages for scheduling reverse link datatransmission for generation in a mobile station or base station,respectively. Various other message types are known in the art and maybe specified in the various communication standards being supported. Themessages are delivered to processor 350 for use in subsequentprocessing. Some or all of the functions of message decoder 330 may becarried out in processor 350, although a discrete block is shown forclarity of discussion. Alternatively, demodulator 325 may decode certaininformation and send it directly to processor 350 (a single bit messagesuch as an ACK/NAK or a power control up/down command are examples). Asan example, a forward link command signal, called the Common CongestionControl subchannel (F-OLCH), may be carried as a subchannel on theForward Common Power Control Channel (F-CPCCH), and can be used toindicate the loading on the reverse link. Various embodiments, describedbelow, detail means for generating this signal for transmission on theforward link, and the corresponding mobile station response fortransmission on the reverse link.

Channel quality estimator 335 is connected to receiver 320, and used formaking various power level estimates for use in procedures describedherein, as well as for use in various other processing used incommunication, such as demodulation. In a mobile station 106, C/Imeasurements may be made. In addition, measurements of any signal orchannel used in the system may be measured in the channel qualityestimator 335 of a given embodiment. As described more fully below,power control channels are another example. In a base station 104 ormobile station 106, signal strength estimations, such as received pilotpower can be made. Channel quality estimator 335 is shown as a discreteblock for clarity of discussion only. It is common for such a block tobe incorporated within another block, such as receiver 320 ordemodulator 325. Various types of signal strength estimates can be made,depending on which signal or which system type is being estimated. Ingeneral, any type of channel quality metric estimation block can bedeployed in place of channel quality estimator 335 within the scope ofthe present invention. In a base station 104, the channel qualityestimates are delivered to processor 350 for use in scheduling, ordetermining the reverse link quality, as described further below.Channel quality estimates may be used to determine whether up or downpower control commands are required to drive either the forward orreverse link power to the desired set point. The desired set point maybe determined with an outer loop power control mechanism, as describedabove.

Signals are transmitted via antenna 310. Transmitted signals areformatted in transmitter 370 according to one or more wireless systemstandards, such as those listed above. Examples of components that maybe included in transmitter 370 are amplifiers, filters,digital-to-analog (D/A) converters, radio frequency (RF) converters, andthe like. Data for transmission is provided to transmitter 370 bymodulator 365. Data and control channels can be formatted fortransmission in accordance with a variety of formats. Data fortransmission on the forward link data channel may be formatted inmodulator 365 according to a rate and modulation format indicated by ascheduling algorithm in accordance with a C/I or other channel qualitymeasurement. A scheduler, such as scheduler 240, described above, mayreside in processor 350. Similarly, transmitter 370 may be directed totransmit at a power level in accordance with the scheduling algorithm.Examples of components which may be incorporated in modulator 365include encoders, interleavers, spreaders, and modulators of varioustypes. A reverse link design, including example modulation formats andaccess control, suitable for deployment on a 1xEV-DV system is alsodescribed below,

Message generator 360 may be used to prepare messages of various types,as described herein. For example, C/I messages may be generated in amobile station for transmission on the reverse link. Various types ofcontrol messages may be generated in either a base station 104 or mobilestation 106 for transmission on the forward or reverse links,respectively. For example, described below are request messages andgrant messages for scheduling reverse link data transmission forgeneration in a mobile station or base station, respectively.

Data received and demodulated in demodulator 325 may be delivered toprocessor 350 for use in voice or data communications, as well as tovarious other components. Similarly data for transmission may bedirected to modulator 365 and transmitter 370 from processor 350. Forexample, various data applications may be present on processor 350, oron another processor included in the wireless communication device 104or 106 (not shown). A base station 104 may be connected, via otherequipment not shown, to one or more external networks, such as theInternet (not shown). A mobile station 106 may include a link to anexternal device, such as a laptop computer (not shown).

Processor 350 may be a general-purpose microprocessor, a digital signalprocessor (DSP), or a special-purpose processor. Processor 350 mayperform some or all of the functions of receiver 320, demodulator 325,message decoder 330, channel quality estimator 335, message generator360, modulator 365, or transmitter 370, as well as any other processingrequired by the wireless communication device. Processor 350 may beconnected with special-purpose hardware to assist in these tasks(details not shown). Data or voice applications may be external, such asan externally connected laptop computer or connection to a network, mayrun on an additional processor within wireless communication device 104or 106 (not shown), or may run on processor 350 itself. Processor 350 isconnected with memory 355, which can be used for storing data as well asinstructions for performing the various procedures and methods describedherein. Those of skill in the art will recognize that memory 355 may becomprised of one or more memory components of various types, that may beembedded in whole or in part within processor 350.

1xEV-DV Reverse Link Design Considerations

In this section, various factors considered in the design of an exampleembodiment of a reverse link of a wireless communication system aredescribed. In many of the embodiments, detailed further in followingsections, signals, parameters, and procedures associated with the1xEV-DV standard are used. This standard is described for illustrativepurposes only, as each of the aspects described herein, and combinationsthereof, may be applied to any number of communication systems withinthe scope of the present invention. This section serves as a partialsummary of various aspects of the invention, although it is notexhaustive. Example embodiments are detailed further in subsequentsections below, in which additional aspects are described.

In many cases, reverse link capacity is interference limited. Basestations allocate available reverse link communication resources tomobile stations for efficient utilization to maximize throughput inaccordance with Quality of Service (QoS) requirements for the variousmobile stations.

Maximizing the use of the reverse link communication resource involvesseveral factors. One factor to consider is the mix of scheduled reverselink transmissions from various mobile stations, each of which may beexperiencing varying channel quality at any given time. To increaseoverall throughput (the aggregate data transmitted by all the mobilestations in the cell), it is desirable for the entire reverse link to befully utilized whenever there is reverse link data to be sent. To fillthe available capacity, mobile stations may be granted access at thehighest rate they can support, and additional mobile stations may begranted access until capacity is reached. One factor a base station mayconsider in deciding which mobile stations to schedule is the maximumrate each mobile can support and the amount of data each mobile stationhas to send. A mobile station capable of higher throughput may beselected instead of an alternate mobile station whose channel does notsupport the higher throughput.

Another factor to be considered is the quality of service required byeach mobile station. While it may be permissible to delay access to onemobile station in hopes that the channel will improve, opting instead toselect a better situated mobile station, it may be that suboptimalmobile stations may need to be granted access to meet minimum quality ofservice guarantees. Thus, the data throughput scheduled may not be theabsolute maximum, but rather maximized considering channel conditions,available mobile station transmit power, and service requirements. It isdesirable for any configuration to reduce the signal to noise ratio forthe selected mix.

Various scheduling mechanisms are described below for allowing a mobilestation to transmit data on the reverse link. One class of reverse linktransmission involves the mobile station making a request to transmit onthe reverse link. The base station makes a determination of whetherresources are available to accommodate the request. A grant can be madeto allow the transmission. This handshake between the mobile station andthe base station introduces a delay before the reverse link data can betransmitted. For certain classes of reverse link data, the delay may beacceptable. Other classes may be more delay-sensitive, and alternatetechniques for reverse link transmission are detailed below to mitigatedelay.

In addition, reverse link resources are expended to make a request fortransmission, and forward link resources are expended to respond to therequest, i.e. transmit a grant. When a mobile station's channel qualityis low, i.e. low geometry or deep fading, the power required on theforward link to reach the mobile may be relatively high. Varioustechniques are detailed below to reduce the number or required transmitpower of requests and grants required for reverse link datatransmission.

To avoid the delay introduced by a request/grant handshake, as well asto conserve the forward and reverse link resources required to supportthem, an autonomous reverse link transmission mode is supported: Amobile station may transmit data at a limited rate on the reverse linkwithout making a request or waiting for a grant.

The base station allocates a portion of the reverse link capacity to oneor more mobile stations. A mobile station that is granted access isafforded a maximum power level. In the example embodiments describedherein, the reverse link resource is allocated using a Traffic to Pilot(T/P) ratio. Since the pilot signal of each mobile station is adaptivelycontrolled via power control, specifying the T/P ratio indicates theavailable power for use in transmitting data on the reverse link. Thebase station may make specific grants to one or more mobile stations,indicating a T/P value specific to each mobile station. The base stationmay also make a common grant to the remaining mobile stations which haverequested access, indicating a maximum T/P value that is allowed forthose remaining mobile stations to transmit. Autonomous and scheduledtransmission, as well as individual and common grants, are detailedfurther below.

Various scheduling algorithms are known in the art, and more are yet tobe developed, which can be used to determine the various specific andcommon T/P values for grants in accordance with the number of registeredmobile stations, the probability of autonomous transmission by themobile stations, the number and size of the outstanding requests,expected average response to grants, and any number of other factors. Inone example, a selection is made based on Quality of Service (QoS)priority, efficiency, and the achievable throughput from the set ofrequesting mobile stations. One example scheduling technique isdisclosed in co-pending U.S. Patent Application No. 60/439,989, entitled“SYSTEM AND METHOD FOR A TIME-SCALABLE PRIORITY-BASED SCHEDULER”, filedJan. 13, 2003, assigned to the assignee of the present invention.Additional references include U.S. Pat. No. 5,914,950, entitled “METHODAND APPARATUS FOR REVERSE LINK RATE SCHEDULING”, and U.S. Pat. No.5,923,650, also entitled “METHOD AND APPARATUS FOR REVERSE LINK RATESCHEDULING”, both assigned to the assignee of the present invention.

A mobile station may transmit a packet of data using one or moresubpackets, where each subpacket contains the complete packetinformation (each subpacket is not necessarily encoded identically, asvarious encoding or redundancy may be deployed throughout varioussubpackets). Retransmission techniques may be deployed to ensurereliable transmission, for example ARQ. Thus, if the first subpacket isreceived without error (using a CRC, for example), a positiveAcknowledgement (ACK) is sent to the mobile station and no additionalsubpackets will be sent (recall that each subpacket comprises the entirepacket information, in one form or another). If the first subpacket isnot received correctly, then a Negative Acknowledgement signal (NAK) issent to the mobile station, and the second subpacket will betransmitted. The base station can combine the energy of the twosubpackets and attempt to decode. The process may be repeatedindefinitely, although it is common to specify a maximum number ofsubpackets. In example embodiments described herein, up to foursubpackets may be transmitted. Thus, the probability of correctreception increases as additional subpackets are received. (Note that athird response from a base station, ACK-and-Continue, is useful forreducing request/grant overhead. This option is detailed further below).

As just described, a mobile station may trade off throughput for latencyin deciding whether to use autonomous transfer to transmit data with lowlatency or requesting a higher rate transfer and waiting for a common orspecific grant. In addition, for a given T/P, the mobile station mayselect a data rate to suit latency or throughput. For example, a mobilestation with relatively few bits for transmission may decide that lowlatency is desirable. For the available T/P (probably the autonomoustransmission maximum in this example, but could also be the specific orcommon grant T/P), the mobile station may select a rate and modulationformat such that the probability of the base station correctly receivingthe first subpacket is high. Although retransmission will be availableif necessary, it is likely that this mobile station will be able totransmit its data bits in one subpacket. In the example embodimentsdescribed herein, each subpacket is transmitted over a period of 5 ms.Therefore, in this example, a mobile station may make an immediateautonomous transfer that is likely to be received at the base stationfollowing a 5 ms interval. Note that, alternatively, the mobile stationmay use the availability of additional subpackets to increase the amountof data transmitted for a given T/P. So, a mobile station may selectautonomous transfer to reduce latency associated with requests andgrants, and may additionally trade the throughput for a particular T/Pto minimize the number of subpackets (hence latency) required. Even ifthe full number of subpackets is selected, autonomous transfer will belower latency than request and grant for relatively small datatransfers. Those of skill in the art will recognize that as the amountof data to be transmitted grows, requiring multiple packets fortransmission, the overall latency may be reduced by switching to arequest and grant format, since the penalty of the request and grantwill eventually be offset by the increased throughput of a higher datarate across multiple packets. This process is detailed further below,with an example set of transmission rates and formats that can beassociated with various T/P assignments.

Mobile stations in varying locations within the cell, and traveling atvarying speeds will experience varying channel conditions. Power controlis used to maintain reverse link signals. Pilot power received at basestation may be power controlled to be approximately equal from variousmobile stations. Then, as described above, the T/P ratio is an indicatorof the amount of the communication resource used during reverse linktransmission. It is desirable to maintain the proper balance betweenpilot and traffic, for a given mobile station transmit power,transmission rate, and modulation format.

Mobile stations may have a limited amount of transmit power available.Thus, for example, the communication rate may be limited by the maximumpower of the mobile station power amplifier. Mobile station transmitpower may also be governed by the base station to avoid excessiveinterference with other mobile stations, using power control and variousdata transmission scheduling techniques. The amount of available mobilestation transmit power will be allocated to transmitting one or morepilot channels, one or more data channels, and any other associatedcontrol channels. To increase data throughput, the rate of transmissionmay be increased by reducing code rate, increasing the symbol rate, orusing a higher order modulation scheme. To be effective, the associatedpilot channel must be received reliably to provide a phase reference fordemodulation. Thus, a portion of the available transmit power isallocated to the pilot, and increasing that portion will increase thereliability of pilot reception. However, increasing the portion ofavailable transmit power allocated to the pilot also decreases theamount of power available for data transmission, and increasing theportion of available transmit power allocated to the data also increasesdemodulation reliability. An appropriate modulation format andtransmission rate can be determined for a given T/P.

Due to variations in data transmission demand, and discontinuousallocation of the reverse link to mobile stations, the transmission ratefor a mobile station may vary rapidly. The desired pilot power level fora transmission rate and format may thus change instantaneously, as justdescribed. Without prior knowledge of rate changes (which may beexpected in the absence of costly signaling or reduced flexibility inscheduling), a power control loop may attempt to counteract a suddenchange in received power at the base station, perhaps interfering withthe decoding of the beginning of the packet. Similarly, due toincremental step sizes commonly deployed in power control, it may take arelatively long time to reduce the pilot once the transmission rate andformat have been reduced. One technique to combat these, and otherphenomena (detailed further below), is to deploy a secondary pilot inaddition to a primary pilot. The primary pilot can be used for powercontrol and demodulation of all channels, including control channels andlow rate data channels. When additional pilot power is needed for higherlevel modulation or increased data rate, additional pilot power may betransmitted on a secondary pilot. The power of the secondary pilot canbe determined relative to the primary pilot and the incremental pilotpower required for the selected transmission. The base station mayreceive both pilots, combine them, and use them to determine phase andmagnitude information for demodulation of the traffic. Instantaneousincreases or decreases in the secondary pilot do not interfere withpower control.

Example embodiments, detailed further below, realize the benefits of asecondary pilot, as just described, by use of an already deployedcommunication channel. Thus, capacity is generally improved, since inpart of the expected range of operation, the information transmitted onthe communication channel requires little or no additional capacity thanrequired to perform the pilot function. As is well known in the art, apilot signal is useful for demodulation because it is a known sequence,and hence the phase and magnitude of the signal may be derived from thepilot sequence for demodulation. However, transmitting pilot withoutcarrying data costs reverse link capacity. Hence, unknown data ismodulated on the “secondary pilot”, and thus the unknown sequence mustbe determined in order to extract information useful for demodulation ofthe traffic signal. In an example embodiment, the Reverse RateIndication Channel (R-RICH) is used to provide the Reverse RateIndicator (RRI), the rate associated with the transmission on theReverse Enhanced Supplemental Channel (R-ESCH). In addition, the R-RICHpower is adjusted in accordance with the pilot power requirements, whichcan be used at the base station to provide a secondary pilot. That theRRI is one of a known set of values aids in determining the unknowncomponent of the R-RICH channel. In an alternate embodiment, any channelmay be modified to serve as a secondary pilot. This technique isdetailed further below.

Reverse Link Data Transmission

One goal of a reverse link design may be to maintain theRise-over-Thermal (RoT) at the base station relatively constant as longas there is reverse link data to be transmitted. Transmission on thereverse link data channel is handled in two different modes:

Autonomous Transmission: This case is used for traffic requiring lowdelay. The mobile station is allowed to transmit immediately, up to acertain transmission rate, determined by the serving base station (i.e.the base station to which the mobile station directs its Channel QualityIndicator (CQI)). A serving base station is also referred to as ascheduling base station or a granting base station. The maximum allowedtransmission rate for autonomous transmission can be signaled by theserving base station dynamically based on system load, congestion, etc.

Scheduled Transmission: The mobile station sends an estimate of itsbuffer size, available power, and possibly other parameters. The basestation determines when the mobile station is allowed to transmit. Thegoal of a scheduler is to limit the number of simultaneoustransmissions, thus reducing the interference between mobile stations.The scheduler may attempt to have mobile stations in regions betweencells transmit at lower rates so as to reduce interference toneighboring cells, and to tightly control RoT to protect the voicequality on the R-FCH, the DV feedback on R-CQICH and the acknowledgments(R-ACKCH), as well as the stability of the system.

Various embodiments, detailed herein, contain one or more featuresdesigned to improve throughput, capacity, and overall system performanceof the reverse link of a wireless communication system. For illustrativepurposes only, the data portion of a 1xEV-DV system, in particular,optimization of transmission by various mobile stations on the EnhancedReverse Supplemental Channel (R-ESCH), is described. Various forward andreverse link channels used in one or more of the example embodiments aredetailed in this section. These channels are generally a subset of thechannels used in a communication system.

FIG. 4 depicts an exemplary embodiment of data and control signals forreverse link data communication. A mobile station 106 is showncommunicating over various channels, each channel connected to one ormore base stations 104A-104C. Base station 104A is labeled as thescheduling base station. The other base stations 104B and 104C are partof the Active Set of mobile station 106. There are four types of reverselink signals and two types of forward link signals shown. They aredescribed below.

R-REQCH

The Reverse Request Channel (R-REQCH) is used by the mobile station torequest from the scheduling base station a reverse link transmission ofdata. In the example embodiment, requests are for transmission on theR-ESCH (detailed further below). In the example embodiment, a request onthe R-REQCH includes the T/P ratio the mobile station can support,variable according to changing channel conditions, and the buffer size(i.e. the amount of data awaiting transmission). The request may alsospecify the Quality of Service (QoS) for the data awaiting transmission.Note that a mobile station may have a single QoS level specified for themobile station, or, alternately, different QoS levels for differenttypes of service options. Higher layer protocols may indicate the QoS,or other desired parameters (such as latency or throughput requirements)for various data services. In an alternative embodiment, a ReverseDedicated Control Channel (R-DCCH), used in conjunction with otherreverse link signals, such as the Reverse Fundamental Channel (R-FCH)(used for voice services, for example), may be used to carry accessrequests. In general, access requests may be described as comprising alogical channel, i.e. a Reverse Schedule Request Channel (r-srch), whichmay be mapped onto any existing physical channel, such as the R-DCCH.The example embodiment is backward compatible with existing CDMA systemssuch as cdma2000® Revision C, and the R-REQCH is a physical channel thatcan be deployed in the absence of either the R-FCH or the R-DCCH. Forclarity, the term R-REQCH is used to describe the access request channelin embodiment descriptions herein, although those of skill in the artwill readily extend the principles to any type of access request system,whether the access request channel is logical or physical. The R-REQCHmay be gated off until a request is needed, thus reducing interferenceand conserving system capacity.

In the example embodiment, the R-REQCH has 12 input bits, that consistof the following: 4 bits to specify the maximum R-ESCH T/P ratio thatthe mobile can support, 4 bits to specify the amount of data in themobile's buffer, and 4 bits to specify the QoS. Those of skill in theart will recognize that any number of bits and various other fields maybe included in alternate embodiments.

F-GCH

The Forward Grant Channel (F-GCH) is transmitted from the schedulingbase station to the mobile station. The F-GCH may be comprised ofmultiple channels. In the example embodiment, a common. F-GCH channel isdeployed for making common grants, and one or more individual F-GCHchannels are deployed for making individual grants. Grants are made bythe scheduling base station in response to one or more requests from oneor more mobile stations on their respective R-REQCHs. Grant channels maybe labeled as GCHx, where the subscript x identifies the channel number.A channel number 0 may be used to indicate the common grant channel. IfN individual channels are deployed, the subscript x may range from 1 toN.

An individual grant may be made to one or more mobile stations, each ofwhich gives permission to the identified mobile station to transmit onthe R-ESCH at a specified T/P ratio or below. Making grants on theforward link will naturally introduce overhead that uses some forwardlink capacity. Various options for mitigating the overhead associatedwith grants are detailed herein, and other options will be apparent tothose of skill in the art in light of the teachings herein.

One consideration is that mobile stations will be situated such thateach experiences varying channel quality. Thus, for example, a highgeometry mobile station with a good forward and reverse link channel mayneed a relatively low power for grant signal, and is likely to be ableto take advantage of a high data rate, and hence is desirable for anindividual grant. A low geometry mobile station, or one experiencingdeeper fading, may require significantly more power to receive anindividual grant reliably. Such a mobile station may not be the bestcandidate for an individual grant. A common grant for this mobilestation, detailed below, may be less costly in forward link overhead.

In the example embodiment, a number of individual F-GCH channels aredeployed to provide the corresponding number of individual grants at aparticular time. The F-GCH channels are code division multiplexed. Thisfacilitates the ability to transmit each grant at the power levelrequired to reach just the specific intended mobile station. In analternative embodiment, a single individual grant channel may bedeployed, with the number of individual grants time multiplexed. To varythe power of each grant on a time multiplexed individual F-GCH mayintroduce additional complexity. Any signaling technique for deliveringcommon or individual grants may be deployed within the scope of thepresent invention.

In some embodiments, a relatively large number of individual grantchannels (i.e. F-GCHs) are deployed, it may be deployed to allow for arelatively large number of individual grants at one time. In such acase, it may be desirable to limit the number of individual grantchannels each mobile station has to monitor. In one example embodiment,various subsets of the total number of individual grant channels aredefined. Each mobile station is assigned a subset of individual grantchannels to monitor. This allows the mobile station to reduce processingcomplexity, and correspondingly reduce power consumption. The tradeoffis in scheduling flexibility, since the scheduling base station may notbe able to arbitrarily assign sets of individual grants (e.g., allindividual grants can not be made to members of a single group, sincethose members, by design, do not monitor one or more of the individualgrant channels). Note that this loss of flexibility does not necessarilyresult in a loss of capacity. For illustration, consider an exampleincluding four individual grant channels. The even numbered mobilestations may be assigned to monitor the first two grant channels, andthe odd numbered mobile stations may be assigned to monitor the lasttwo. In another example, the subsets may overlap, such as the evenmobile stations monitoring the first three grant channels, and the oddmobile stations monitoring the last three grant channels. It is clearthat the scheduling base station cannot arbitrarily assign four mobilestations from any one group (even or odd). These examples areillustrative only. Any number of channels with any configuration ofsubsets may be deployed within the scope of the present invention.

The remaining mobile stations, having made a request, but not receivingan individual grant, may be given permission to transmit on the R-ESCHusing a common grant, which specifies a maximum T/P ratio that each ofthe remaining mobile stations must adhere to. The common F-GCH may alsobe referred to as the Forward Common Grant Channel (F-CGCH). A mobilestation monitors the one or more individual grant channels (or a subsetthereof) as well as the common F-GCH. Unless given an individual grant,the mobile station may transmit if a common grant is issued. The commongrant indicates the maximum T/P ratio at which the remaining mobilestations (the common grant mobile stations) may transmit for the datawith certain type of QoS.

In the example embodiment, each common grant is valid for a number ofsubpacket transmission intervals. Once receiving a common grant, amobile station which has sent a request, but doesn't get an individualgrant may start to transmit one or more encoder packets within thesubsequent transmission intervals. The grant information may be repeatedmultiple times. This allows the common grant to be transmitted at areduced power level with respect to an individual grant. Each mobilestation may combine the energy from multiple transmissions to reliablydecode the common grant. Therefore, a common grant may be selected formobile stations with low-geometry, for example, where an individualgrant is deemed too costly in terms of forward link capacity. However,common grants still require overhead, and various techniques forreducing this overhead are detailed below.

The F-GCH is sent by the base station to each mobile station that thebase station schedules for transmission of a new R-ESCH packet. It mayalso be sent during a transmission or a retransmission of an encoderpacket to force the mobile station to modify the T/P ratio of itstransmission for the subsequent subpackets of the encoder packet in casecongestion control becomes necessary.

Detailed below are examples of timing, including various embodimentswith requirements for the interrelationship of access requests andgrants of either type (individual or common). Additionally, techniquesfor reducing the number of grants, and thus the associated overhead, aswell as for congestion control are detailed below.

In the example embodiment, the common grant consists of 12 bitsincluding a 3-bit type field to specify the format of the next ninebits. The remaining bits indicate the maximum allowed T/P ratio for 3classes of mobiles as specified in the type field, with 3 bits denotingthe maximum allowable T/P ratio for each class. The mobile classes maybe based on QoS requirements, or other criterion. Various other commongrant formats are envisioned, and will be readily apparent to one ofordinary skill in the art.

In the example embodiment, an individual grant comprises 12 bitsincluding: 11 bits to specify the Mobile ID and maximum allowed T/Pratio for the mobile station being granted to transmit, or to explicitlysignal the mobile station to change its maximum allowed T/P ratio,including setting the maximum allowed T/P ratio to 0 (i.e., telling themobile station not to transmit the R-ESCH). The bits specify the MobileID (1 of 192 values) and the maximum allowed T/P (1 of 10 values) forthe specified mobile. In an alternate embodiment, 1 long-grant bit maybe set for the specified mobile. When the long-grant bit is set to one,the mobile station is granted permission to transmit a relatively largefixed, predetermined number (which can be updated with signaling) ofpackets on that ARQ channel. If the long-grant bit is set to zero, themobile station is granted to transmit one packet. A mobile may be toldto turn off its R-ESCH transmissions with the zero T/P ratiospecification, and this may be used to signal the mobile station to turnoff its transmission on the R-ESCH for a single subpacket transmissionof a single packet if the long-grant bit is off or for a longer periodif the long-grant bit is on.

R-PICH

The Reverse Pilot Channel (R-PICH) is transmitted from the mobilestation to the base stations in the Active Set. The power in the R-PICHmay be measured at one or more base stations for use in reverse linkpower control. As is well known in the art, pilot signals may be used toprovide amplitude and phase measurements for use in coherentdemodulation. As described above, the amount of transmit power availableto the mobile station (whether limited by the scheduling base station orthe inherent limitations of the mobile station's power amplifier) issplit among the pilot channel, traffic channel or channels, and controlchannels. Additional pilot power may be needed for higher data rates andmodulation formats. To simplify the use of the R-PICH for power control,and to avoid some of the problems associated with instantaneous changesin required pilot power, an additional channel may be allocated for useas a supplemental or secondary pilot. Although, generally, pilot signalsare transmitted using known data sequences, as disclosed herein, aninformation bearing signal may also be deployed for use in generatingreference information for demodulation. In an example embodiment, theR-RICH (detailed below) is used to carry the additional pilot powerdesired.

R-RICH

The Reverse Rate Indicator Channel (R-RICH) is used by the mobilestation to indicate the transmission format on the reverse trafficchannel, R-ESCH. The R-RICH comprises 5-bit messages. The orthogonalencoder block maps each 5-bit input sequence into a 32-symbol orthogonalsequence. For example each 5-bit input sequence could be mapped to adifferent Walsh code of length 32. A sequence repetition block repeatsthe sequence of 32 input symbols three times. A bit repetition blockprovides at its output the input bit repeated 96 times. A sequenceselector block selects between the two inputs, and passes that input tothe output. For zero rates, the output of the bit repetition block ispassed through. For all other rates, the output of the sequencerepetition block is passed through. A signal point mapping block maps aninput bit 0 to +1, and an input 1 to −1. Following the signal pointmapping block is a Walsh spreading block. The Walsh spreading blockspreads each input symbol to 64 chips. Each input symbols multiplies aWalsh code W(48, 64). A Walsh code W(48,64) is the Walsh code of length64 chips, and index 48. TIA/EIA IS-2000 provides tables describing Walshcodes of various lengths.

Those of skill in the art will recognize that this channel structure isone example only. Various other encoding, repetition, interleaving,signal point mapping, or Walsh encoding parameters could be deployed inalternate embodiments. Additional encoding or formatting techniques,well known in the art, may also be deployed. These modifications fallwithin the scope of the present invention.

R-ESCH

The Enhanced Reverse Supplemental Channel (R-ESCH) is used as thereverse link traffic data channel in the example embodiments describedherein. Any number of transmission rates and modulation formats may bedeployed for the R-ESCH. In an example embodiment, the R-ESCH has thefollowing properties: Physical layer retransmissions are supported. Forretransmissions when the first code is a Rate ¼ code, the retransmissionuses a Rate ¼ code and energy combining is used. For retransmissionswhen the first code is a rate greater than ¼, incremental redundancy isused. The underlying code is a Rate ⅕ code. Alternatively, incrementalredundancy could also be used for all the cases.

Hybrid Automatic-Repeat-Request (HARQ) is supported for both autonomousand scheduled users, both of which may access the R-ESCH.

For the case in which the first code is a Rate ½ code, the frame isencoded as a Rate ¼ code and the encoded symbols are divided equallyinto two parts. The first half of the symbols are sent in the firsttransmission, the second half in the second transmission, then the firsthalf in the third transmission and so on.

Multiple ARQ-channel synchronous operation may be supported with fixedtiming between the retransmissions: a fixed number of sub-packetsbetween consecutive sub-packets of same packet may be allowed.Interlaced transmissions are allowed as well. As an example, for 5 msframes, 4 channel ARQ could be supported with 3 subpacket delay betweensubpackets.

Table 1 lists example data rates for the Enhanced Reverse SupplementalChannel. A 5 ms subpacket size is described, and the accompanyingchannels have been designed to suit this choice. Other subpacket sizesmay also be chosen, as will be readily apparent to those of skill in theart. The pilot reference level is not adjusted for these channels, i.e.the base station has the flexibility of choosing the T/P to target agiven operating point. This max T/P value is signaled on the ForwardGrant Channel. The mobile station may use a lower T/P if it is runningout of power to transmit, letting HARQ meet the required QoS. Layer 3signaling messages may also be transmitted over the R-ESCH, allowing thesystem to operate without the R-FCH and/or R-DCCH.

TABLE 1 Enhanced Reverse Supplemental Channel Parameters Number SymbolEffective of Number Repetition Number of Code Bits per of Data FactorBinary Code Rate Encoder 5-ms Data Rate Rate/ Code Before the WalshSymbols in All Including Packet Slots (kbps) 9.6 kbps Rate InterleaverModulation Channels the Subpackets Repetition 192 4 9.6 1.000 ¼ 2 BPSKon 1 ++−− 6,144 1/32 192 3 12.8 1.333 ¼ 2 BPSK on 1 ++−− 4,608 1/24 1922 19.2 2.000 ¼ 2 BPSK on 1 ++−− 3,072 1/16 192 1 38.4 4.000 ¼ 2 BPSK on1 ++−− 1,536 ⅛ 384 4 19.2 2.000 ¼ 1 BPSK on 1 ++−− 6,144 1/16 384 3 25.62.667 ¼ 1 BPSK on 1 ++−− 4,608 1/12 384 2 38.4 4.000 ¼ 1 BPSK on 1 ++−−3,072 ⅛ 384 1 76.8 8.000 ¼ 1 BPSK on 1 ++−− 1,536 ¼ 768 4 76.8 4.000 ¼ 1QPSK ++−− 12,288 1/16 768 3 102.4 5.333 ¼ 1 QPSK ++−− 9,216 1/12 768 2153.6 8.000 ¼ 1 QPSK ++−− 6,144 ⅛ 768 1 307.2 16.000 ¼ 1 QPSK ++−− 3,072¼ 1,536 4 76.8 8.000 ¼ 1 QPSK +− 24,576 1/16 1,536 3 102.4 10.667 ¼ 1QPSK +− 18,432 1/12 1,536 2 153.6 16.000 ¼ 1 QPSK +− 12,288 ⅛ 1,536 1307.2 32.000 ¼ 1 QPSK +− 6,144 ¼ 2,304 4 115.2 12.000 ¼ 1 QPSK ++−−/+−36,864 1/16 2,304 3 153.6 16.000 ¼ 1 QPSK ++−−/+− 27,648 1/12 2,304 2230.4 24.000 ¼ 1 QPSK ++−−/+− 18,432 ⅛ 2,304 1 460.8 48.000 ¼ 1 QPSK++−−/+− 9,216 ¼ 3,072 4 153.6 16.000 ⅕ 1 QPSK ++−−/+− 36,864 1/12 3,0723 204.8 21.333 ⅕ 1 QPSK ++−−/+− 27,648 1/9 3,072 2 307.2 32.000 ⅕ 1 QPSK++−−/+− 18,432 ⅙ 3,072 1 614.4 64.000 ⅕ 1 QPSK ++−−/+− 9,216 ⅓ 4,608 4230.4 24.000 ⅕ 1 QPSK ++−−/+− 36,864 ⅛ 4,608 3 307.2 32.000 ⅕ 1 QPSK++−−/+− 27,648 ⅙ 4,608 2 460.8 48.000 ⅕ 1 QPSK ++−−/+− 18,432 ¼ 4,608 1921.6 96.000 ⅕ 1 QPSK ++−−/+− 9,216 ½ 6,144 4 307.2 32.000 ⅕ 1 QPSK++−−/+− 36,864 ⅙ 6,144 3 409.6 42.667 ⅕ 1 QPSK ++−−/+− 27,648 2/9 6,1442 614.4 64.000 ⅕ 1 QPSK ++−−/+− 18,432 ⅓ 6,144 1 1228.8 128.000 ⅕ 1 QPSK++−−/+− 9,216 ⅔

In an example embodiment, turbo coding is used for all the rates. WithR=¼ coding, an interleaver similar to the current cdma2000 reverse linkis used. With R=⅕ coding, an interleaver similar to the cdma2000 ForwardPacket Data Channel is used.

The number of bits per encoder packet includes the CRC bits and 6 tailbits. For an encoder packet size of 192 bits, a 12-bit CRC is used;otherwise, a 16-bit CRC is used. The 5-ms slots are assumed to beseparated by 15 ms to allow time for ACK/NAK responses. If an ACK isreceived, the remaining slots of the packet are not transmitted.

The 5 ms subpacket duration, and associated parameters, just described,serve as an example only. Any number of combinations of rates, formats,subpacket repetition options, subpacket duration, etc. will be readilyapparent to those of skill in the art in light of the teaching herein.An alternate 10 ms embodiment, using 3 ARQ channels, could be deployed.In one embodiment, a single subpacket duration or frame size isselected. For example, either a 5 ms or 10 ms structure would beselected. In an alternate embodiment, a system may support multipleframe durations.

F-CACKCH

The Forward Common Acknowledgement Channel, or F-CACKCH, is used by thebase station to acknowledge the correct reception of the R-ESCH, as wellas to extend an existing grant. An acknowledgement (ACK) on the F-CACKCHindicates correct reception of a subpacket. Additional transmission ofthat subpacket by the mobile station is unnecessary. The negativeacknowledgement (NAK) on the F-CACKCH allows the mobile station totransmit the next subpacket up to the maximum allowed number ofsubpacket per packet. A third command, the ACK-and-Continue, allows thebase station to acknowledge successful reception of a packet and, at thesame time, permit the mobile station to transmit using the grant thatled to the successfully received packet. One embodiment of the F-CACKCHuses +1 values for the ACK symbols, NULL symbols for the NAK symbols,and −1 values for the ACK-and-Continue symbols. In various exampleembodiments, detailed further below, up to 96 Mobile IDs can besupported on one F-CACKCH. Additional F-CACKCHs may be deployed tosupport additional Mobile IDs.

On-off keying (i.e., not sending NAK) on the F-CACKCH allows the basestations (especially non-scheduling base stations) an option of notsending the ACK when the cost (required power) of doing so is too high.This provides the base station a trade-off between the forward link andreverse link capacity, since a correctly received packet that is notACKed will likely trigger a re-transmission at a later point in time.

A Hadamard Encoder is one example of an encoder for mapping onto a setof orthogonal functions. Various other techniques may also be deployed.For example, any Walsh Code or other similar error correcting code maybe used to encode the information bits. Different users may betransmitted to at different power levels if independent each subchannelhas an independent channel gain. The F-CACKCH conveys one dedicatedtri-valued flag per user. Each user monitors the F-ACKCH from all basestations in its Active Set (or, alternatively, signaling may define areduced active set to reduce complexity).

In various embodiments, two channels are each covered by a 128-chipWalsh cover sequence. One channel is transmitted on the I channel, andthe other is transmitted on the Q channel. Another embodiment of theF-CACKCH uses a single 128-chip Walsh cover sequence to support up to192 mobile stations simultaneously. This approach uses 10-ms durationfor each tri-valued flag.

There are several ways of operating the ACK channel. In one embodiment,it may be operated such that a “1” is transmitted for an ACK. Notransmission implies a NAK, or the “off” state. A “−1” transmissionrefers to ACK-and-Continue, i.e. the same grant is repeated to themobile station. This saves the overhead of a new grant channel.

To review, when the mobile station has a packet to send that requiresusage of the R-ESCH, it sends the request on the R-REQCH. The basestation may respond with a grant using the F-CGCH, or an F-GCH. However,this operation is somewhat expensive. To reduce the forward linkoverhead, F-CACKCH can send the “ACK-and-Continue” flag, which extendsthe existing grant at low cost by the scheduling base station. Thismethod works for both individual and common grants. ACK-and-Continue isused from the granting base station, and extends the current grant for 1more encoder packet on the same ARQ channel.

Note that, as shown in FIG. 4, not every base station in the Active Setis required to send back the F-CACKCH. The set of base stations sendingthe F-CACKCH in soft handoff may be a subset of the Active Set. Exampletechniques for transmitting the F-CACKCH are disclosed in co-pendingU.S. patent application Ser. No. 10/611,333, entitled “CODE DIVISIONMULTIPLEXING COMMANDS ON A CODE DIVISION MULTIPLEXED CHANNEL”, filedJun. 30, 2003, assigned to the assignee of the present invention(hereinafter the 'AAA application).

F-CPCCH

The Forward Common Power Control Channel (F-CPCCH) is used to powercontrol various reverse link channels, including the R-ESCH when theF-FCH and the F-DCCH are not present. Upon channel assignment, a mobilestation is assigned a reverse link power control channel. The F-CPCCHmay contain a number of power control subchannels.

The F-CPCCH carries a power control subchannel called the CommonCongestion Control subchannel (F-OLCH). The congestion controlsubchannel is typically at a rate of 100 bps, though other rates can beused. The single bit (which may be repeated for reliability), referredto herein as the busy bit, indicates the mobile stations in autonomoustransmission mode, or in the common grant mode, or both, whether toincrease or decrease their rate. In an alternate embodiment, individualgrant modes may be also be sensitive to this bit. Various embodimentsmay be deployed with any combination of transmission types responsive tothe F-OLCH (detailed further below). This can be done in a probabilisticmanner, or deterministically.

In one embodiment, setting the busy bit to ‘0’ indicates that mobilestations responsive to the busy bit should decrease their transmissionrate. Setting the busy bit to ‘1’ indicates a corresponding increase intransmission rate. Myriad other signaling schemes may be deployed, aswill be readily apparent to those of skill in the art, and variousalternate examples are detailed below.

During channel assignment, the mobile station is assigned to thesespecial power control channels. A power control channel may control allthe mobiles in the system, or alternatively, varying subsets of themobile stations may be controlled by one or more power control channels.Note that use of this particular channel for congestion control is butone example. The techniques described herein may be used with any meansfor signaling, as will be detailed further below.

Example Congestion Control Embodiments

To summarize various features introduced above, mobile stations areauthorized to make autonomous transmissions, which, while perhapslimited in throughput, allow for low delay. In such a case, the mobilestation may transmit without request up to a max R-ESCH T/P ratio,T/PMax_auto, which may be set and adjusted by the base station throughsignaling.

Scheduling is determined at one or more scheduling base stations, andallocations of reverse link capacity are made through grants transmittedon the F-GCH at a relatively high rate. Scheduling may thus be employedto tightly control the reverse link load and thus protects voice quality(R-FCH), DV feedback (R-CQICH) and DV acknowledgement (R-ACKCH).

An individual grant allows detailed control of a mobile station'stransmission. Mobile stations may be selected based upon geometry andQoS to maximize throughput while maintaining required service levels. Acommon grant allows efficient notification, especially for low geometrymobile stations.

The F-CACKCH channel may send “ACK-and-Continue” commands, which extendexisting grants at low cost. This works with both individual grants andcommon grants. Various embodiments and techniques for scheduling,granting, and transmitting on a shared resource, such as a 1xEV-DVreverse link, are disclosed in U.S. Pat. No. 7,155,236, entitled“SCHEDULED AND AUTONOMOUS TRANSMISSION AND ACKNOWLEDGEMENT”, filed Aug.21, 2003, assigned to the assignee of the present invention, andincorporated by reference herein.

FIG. 5 contrasts the R-ESCH power level with and without fast control.During transmission on the R-ESCH, each mobile station transmits inaccordance with the rate granted on the R-GCH (i.e., an individualgrant), or R-CGCH (i.e., a common grant), or transmits autonomously. Themobile station can transmit up to the maximum rate that is permitted. Ifthe R-ESCH that the mobile station is using has been assigned acongestion control subchannel (F-OLCH), then the mobile station adjuststhe transmission rate based upon the bits that are received in thecongestion control subchannel.

There are a variety of ways to do this. If all the mobiles areclassified into three classes: autonomous, common granted, orindividually granted, then this channel may be applicable to all users,only on one class of users, or to any two classes of users depending onthe level of control desired.

If the mobiles controlled by the F-CGCH change rates probabilistically,it may not be necessary to add an additional bit on the F-CPCCH. Thisinformation (i.e., the busy bit) may be sent on the F-CGCH. The absenceof a busy bit may be interpreted by mobile stations as a license toincrease to the maximum rate allowed. Alternatively, mobile stations mayalso be allowed to go up probabilistically. Various examples aredetailed below.

FIG. 6 depicts a method 600 of congestion control that may be performedin a base station. The process begins in step 610, where a serving basestation, such as base station 104, allocates resources and makes grants,when applicable, to one or more mobile stations. The resources allocatedmay be a portion of a shared communication resource, as described above.The allocation may be computed using any requests for transmissionreceived, as well as the expected amount of autonomous transmission,which may be based on statistical models, the number of mobile stationsregistered in the base station's coverage area, past autonomoustransmission, etc. Individual and/or common grants may be allocated toone or more mobile stations, and the resultant messages may betransmitted to those mobile stations, as described above.

In step 620, the base station measures the system load. The loading onthe system may be due to a previous allocation of resources, such asdescribed with respect to step 610, as well as autonomous transmission.The system load may be more or less than anticipated when the previousallocation of resources was made. For example, the expected number ofautonomous transmissions may be greater than or less than the amount ofactual autonomous transmissions. Other factors, such as changes inchannel conditions, a missed mobile station request (and subsequenttransmission by that mobile station in response to a common grant), andother factors may cause the measured system loading to be higher orlower than is desired by the base station at a given time. One moresource of variation is changes in the other cell interference thatvaries unpredictably. The base station often uses a margin to accountfor such unexpected behavior.

In decision block 630, based on the current measured conditions, if thebase station decides that the system is exceeding the desired loading onthe shared resource (The R-ESCH, in this example embodiment), proceed tostep 640. Otherwise, return to step 610 to reallocate resources for thenext time duration. If a previously asserted busy signal is asserted, itmay be deasserted. In step 640, when the system is determined to bebusy, a busy signal is asserted to indicate a need for reduced loading.The busy condition may be signaled to mobile stations in any of avariety of ways. In one embodiment, as described above, a busy bit isset on the F-OLCH. This channel is multiplexed onto the F-CPCCH. Inanother example, the F-OLCH could be multiplexed on another channel in aCDM on CDM manner, or be a separate physical channel, as described inthe aforementioned 'AAA application. Mobile stations in the system mayrespond to an asserted busy signal in a variety of ways. Exampleembodiments are detailed further below.

FIG. 7 depicts a generalized method 700 of congestion control performedat a mobile station. The process begins in decision block 710, if thesystem is identified as being busy, using any of the signalingtechniques described above, such as a busy bit or busy signal, themobile station proceeds to step 720 and reduces its rate (there maylimitations as to when or how low to reduce the rate, examples aredetailed below.) For example, mobile stations receiving the busy signalmay reduce their rate all at once with a fixed rate reduction, using aprobabilistic method to determine whether or not to reduce, using aprobabilistic method to determine by how much to reduce the rate, and soforth. The rate reduction values may be pre-determined, or updatedduring a communication session using signaling. Different mobilestations may use different mechanisms to determine how to reduce theirrates. For example, mobile stations with a higher QoS designation may beless likely to reduce, or reduce a lower amount, than a relatively lowerQoS designated mobile station. Note that a mobile station transmittingunder an individual or common grant may alter its transmission rate inresponse to a busy signal, as well as a mobile station transmittingautonomously. Any subclass of the mobile stations may be programmed torespond to a busy signal in a different way than any other subclass. Forexample, individual grants may not be designated for reduction, while acommon grant is. Or both types may be designated for reduction, atdifferent levels. QoS designations may determine the varying subclasses.Or, each mobile station may be signaled with its own unique parametersfor responding to a busy signal with congestion control countermeasures.There are myriad combinations, some of which are described in exampleembodiments below, which will be readily apparent to those of skill inthe art and fall within the scope of the present invention.

If the busy signal is not asserted, in decision block 710, proceed tostep 730 and transmit at the determined rate. This rate may bedetermined in a variety of ways. The rate may be signaled using a commonor individual grant, or may be the rate indicated as the maximum ratefor autonomous transmission. Any of these example rates may have beenreduced, as just described, in a previous iteration of method 700, andthus the determined rate reflects this reduction. A previously reducedrate may be increased once the busy signal is no longer asserted, eitherat a deterministic or probabilistic rate. Examples will be detailedbelow.

Note that, in general, the mechanisms for providing a common orindividual grant may also be used for congestion control. For example, acommon grant may be reissued at a lower rate. Or, an ACK (but notcontinue) command may be sent, followed by a lower individual grant tothe respective mobile station. Similarly, an autonomous transmissionmaximum rate may be adjusted through signaling. These techniques requirea relatively higher amount of overhead than setting a busy bit, withpotentially longer latency in response. Thus, setting the busy bitallows the serving base station to work through a temporal increase insystem load without the need to regnant. Nonetheless, selectivelyregranting (or removing previous grants, i.e. sending an ACK instead ofan ACK-and-Continue), as described above, may be used in conjunctionwith the busy bit, as will be apparent to those of skill in the art.

FIG. 8 depicts a method 800 of congestion control with set rate limits.The process begins in decision block 810, where, if the busy signal isasserted, proceed to decision block 820. If the busy signal is notasserted, proceed to decision block 840. In decision block 840, if themobile station is transmitting at the maximum allowed rate, proceed tostep 860 to continue transmission at the current rate. The maximumallowed rate may be dependent upon the type of transmission beingperformed. The rate may be set as identified in an individual grant tothe mobile station, a common grant on which the mobile station may rely,or may be the maximum allowed rate for autonomous transmission. If thecurrent rate is less than the maximum allowed rate (due to a previousresponse to a busy condition, for example), proceed to step 850 toincrease the rate. Then proceed to step 860 to transmit at thedetermined rate. An example technique for increasing and decreasingrates in accordance with rate limits is detailed further below withrespect to FIG. 10.

In decision block 810, if the busy signal is asserted, proceed todecision block 820. If the mobile station is transmitting at the minimumspecified rate, then proceed to step 860 to continue transmission atthat rate. If not, proceed to step 830, reduce the rate, then proceed tostep 860 and resume transmission at the adjusted rate. Note that thereduction or increase of rate in steps 830 or 850, respectively, may bedeterministic or probabilistic.

In an alternate embodiment, details not shown, the mobile station maybegin transmission at a rate other than the maximum specified. Forexample, a common grant may allow for a specified maximum rate. A mobilestation may begin transmission at a lower rate, then increase its rateprobabilistically or deterministically until the specified maximum rateis reached, as described in FIG. 8.

FIG. 9 depicts a method 900 of congestion control using a tri-valuedbusy signal. For example, a busy signal may contain one of three values,a first value to indicate the shared resource is underutilized, or thatrates may increase, a second value to indicate the resource isoverutilized, or that rates should decrease, and a third value toindicate that neither increases or decreases are desired. A tri-valuedsignal similar to the F-CACKCH may be deployed in one embodiment. Anincrease is signaled by transmitting a positive value, a decrease issignaled by transmitting a negative value, and no transmission indicatesthat neither an increase nor a decrease should be performed. Any othermulti-valued signal may also be deployed, as will be apparent to thoseof skill in the art.

The process begins in decision block 910. If a mobile station receivesan increase value on a busy signal, proceed to step 920 and increase therate. The rate increase may be probabilistic or deterministic, and mayinclude a maximum rate limit, as described above with respect to FIG. 8.Then the mobile station transmits at the determined rate in step 950.One example situation in which a rate increase may be signaled isfollowing a previous rate decrease signaled on the busy signal in orderto reduce congestion. When the congestion is relieved, it may be usefulto reverse the effects of the rate decreases.

If a mobile station does not receive an increase value on the busysignal in decision block 910, proceed to decision block 930. If adecrease is received on the busy signal, proceed to step 940 anddecrease the rate. The rate decrease may be probabilistic ordeterministic, and may include a minimum rate limit, as described abovewith respect to FIG. 8. Then the mobile station transmits at thedetermined rate in step 950. A rate decrease signal may be used toreduce congestion on the shared resource.

If neither an increase nor decrease is received by the mobile station,then the current rate is used and the mobile station transmits at thedetermined rate in step 950. After transmission, the process returns todecision block 910 for the next iteration, in which a new value may betransmitted on the busy signal.

In an alternate embodiment, not shown, a multi-valued busy signal may bedeployed using more than three values. Additional values may indicatevarying levels of increase or decrease, and a mobile station mayincrease or decrease with a varying rate difference based on therespective signal received. For example, one value may indicate anincrease to the maximum rate allowed, while another value indicates anintermediate incremental increase (which may ultimately be limited bythe maximum rate). Similarly, a third value may indicate an incrementaldecrease, while a fourth value indicates the rate should immediatelyadjust to the minimum rate for the mobile station. A fifth value mayindicate no adjustment is necessary. Myriad combinations of rateadjustment values on the busy signal will be readily deployed by thoseof skill in the art in light of the teachings herein.

FIG. 10 depicts an embodiment of a rate table 1000 that may be deployedwith any congestion control method. In one embodiment, rate table 1000may be deployed in memory 355, described above. In this example, ratetable 1000 comprises N supported rates, where rate 1 is the highestsupported rate and rate N is the lowest supported rate. Variousparameters associated with the rates may also be stored. The rates andassociated parameters may be adjusted through signaling, if necessary,or may be pre-determined and fixed. Rate tables in various mobilestations may be identical, but need not be so.

In the example of FIG. 10, rates have corresponding α and β parametersfor use in probabilistic rate increases and decreases, respectively.Transitions are shown from each rate (except the minimum rate) to alower rate with an associated α value. Similarly, transitions are shownfrom each rate (except the maximum rate) to a higher rate with anassociated β value. When a busy signal indicates an increase ordecrease, a mobile station will make a transition to a higher or lowerrate with probability α or β, respectively. For example, when a mobilestation transmitting at rate 3 receives a decrease signal, then it willlower its rate and transmit at rate 4 with probability α3. It willcontinue to transmit at rate 3, notwithstanding the decrease signal,with probability 1-α3. Similarly, the mobile station transmitting atrate 3, after receiving an increase signal, will increase itstransmission to rate 2 with probability β3. Notwithstanding the increasesignal, it will continue transmitting at rate 3 with probability 1-β3. Adecrease parameter α is stored for each rate except the minimum rate,rate N. An increase parameter β is stored for each rate except themaximum rate, rate 1. Note that each parameter does not need to have aunique value, and can be modified by signaling. In one example, a singleprobability parameter may be used for all increases and decreases fromany rate to the higher or lower rate, respectively. Or, a singleincrease parameter may be used for all rates, and a different decreaseparameter may be used for all rates. Any combination of increase anddecrease parameters may be deployed. Those of skill in the art willrecognize that the storage requirements of rate table 1000 may beadjusted in accordance with the number of unique parameters. The ratetransition parameters may be used in conjunction with a busy signal toprovide congestion control for a base station and any number of mobilestations, as described above.

Also depicted in FIG. 10 are various pointers indicating rate limits,for use in embodiments such as the examples described above. A maximumrate is specified. This rate may correspond to the rate given in a grantfrom the base station, which may be an individual grant or a commongrant. The maximum rate may thus be adjusted through the course ofrequests and grants, as described above.

Also shown is the maximum autonomous rate. This rate may be adjustedthrough signaling. It may be the same for all mobile stations, ordiffering classes of mobile stations may have differing maximumautonomous rates based on QoS levels. A mobile station will know whetherit is transmitting in response to a grant, either individual or common,or whether it is transmitting autonomously. The maximum rate for anygiven mobile station is thus dependent on the type of transmission beingcarried out.

A minimum rate may also be identified. This may be the minimum ratesupported in the rate table 1000, or a higher rate may be specified. Inone embodiment, the minimum supported rate may be used for autonomoustransmission, while a higher minimum rate is used for transmission inresponse to a grant. Thus, the mobile station may limit its ratedecreases in response to a busy signal to differing levels based on thetype of transmission being carried out. Recall that, as described above,a mobile station may be deployed to respond to the busy signal for anytransmission (autonomous or granted), or a subset of the possibletransmission types. For example, individual grants may be exempted fromcongestion control, and the mobile station may perform rate adjustmentin response to the busy signal for common grant transmissions orautonomous transmissions. The common grant transmission rates may thusbe limited, for example, to those rates between the maximum rate and theminimum rate. The autonomous transmission rates may be limited to thoserates between the minimum supported rate (rate N) and the maximumautonomous rate (rate M, in this example). The rate adjustment may beperformed using any congestion control method, examples of which aredescribed above with respect to FIGS. 6-9.

It should be noted that in all the embodiments described above, methodsteps can be interchanged without departing from the scope of theinvention. The descriptions disclosed herein have in many cases referredto signals, parameters, and procedures associated with the 1xEV-DVstandard, but the scope of the present invention is not limited as such.Those of skill in the art will readily apply the principles herein tovarious other communication systems. These and other modifications willbe apparent to those of ordinary skill in the art.

Those of skill in the art will understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill will further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. An apparatus, operable with a plurality of remote stations capable oftransmission on a shared resource, comprising: a receiver for receivinga plurality of access requests for transmission on the shared resourcefrom a respective plurality of remote stations and for measuring theutilization of the shared resource; a scheduler for allocating a portionof the shared resource to zero or more of the requesting remote stationsin response to the plurality of access requests, the allocationcomprising zero or one common access grant to a subset of the requestingremote stations and for generating a multi-valued busy signal inresponse to the measured utilization; and a transmitter for transmittingthe common access grant to the remaining remote stations on one or morecommon grant channels and for transmitting the multi-valued busy signal.2. The apparatus of claim 1, wherein: the scheduler further allocateswith an allocation further comprising zero or more individual accessgrants to zero or more requesting remote stations; and the transmitterfurther transmits the individual access grants to the respective remotestations on one or more individual grant channels.
 3. The apparatus ofclaim 1, further operable with the plurality of remote stations equippedto transmit autonomously on the shared resource, using a limited portionof the shared resource, without an access request or access grant, andwherein: the scheduler computes the expected amount of the sharedresource to be consumed by the autonomous transmissions and allocatesthe portion of the shared resource for individual and common accessgrants in response thereto.
 4. The apparatus of claim 1, furtheroperable with one or more remote stations transmitting with permissionfrom one or more access grants, the apparatus further comprising: adecoder for decoding one or more received packets and determining if theone or more received packets decoded without error; and wherein: thereceiver further receives the one or more packets of data from one ormore remote stations, respectively; the transmitter further transmits tothe one or more remote stations an acknowledgment and grant extension(ACK-and-Continue) command, respectively, when the respective receivedpacket decoded without error and the access grant for the respectiveremote station is to be extended; and the scheduler determines theallocation of the portion of the shared resource in accordance withindividual and common grants extended with the one or moreACK-and-Continue commands.
 5. A remote station, comprising: a databuffer for receiving data for transmission; a message generator forgenerating an access request message when the data buffer contains datafor transmission; a receiver for receiving one or more common grantchannels from a base station and for receiving a multi-valued busysignal from the base station; a message decoder for decoding an accessgrant directed to the remote station, the access grant comprising acommon grant on one of the one or more common grant channels; and atransmitter for transmitting the access request message and fortransmitting a portion of data from the data buffer in response to adecoded access grant in accordance with the received multi-valued busysignal.
 6. The remote station of claim 5, wherein: the receiver furtherreceives one or more individual grant channels from the base station;and the message decoder further decodes an access grant comprising anindividual grant directed on one of the one or more individual grantchannels.
 7. The remote station of claim 5, wherein the transmitterfurther transmits a limited portion of the data in the data bufferautonomously, irrespective of whether an access grant has been received,responsive to the received busy signal.
 8. The remote station of claim5, wherein: the receiver further receives an ACK-and-Continue command;and the transmitter transmits an additional portion of data from thedata buffer in response to a previously decoded access grant, responsiveto the received busy signal.
 9. The remote station of claim 5, whereinthe transmitter further transmits a limited portion of the data in thedata buffer autonomously, subsequent to a received ACK, responsive tothe received busy signal.
 10. The remote station of claim 5, wherein:the receiver further receives a NAK command; and the transmitterretransmits the portion of data from the data buffer previouslytransmitted in response to a previously decoded access grant, responsiveto the received busy signal.
 11. The remote station of claim 5, whereinthe transmission rate is decreased in response to an assertion on thereceived busy signal.
 12. The remote station of claim 11, wherein thedecrease is deterministic.
 13. The remote station of claim 11, whereinthe decrease is probabilistic.
 14. The remote station of claim 9,wherein the transmission rate is increased in response to an assertionon the received busy signal.
 15. The remote station of claim 14, whereinthe increase is deterministic.
 16. The remote station of claim 14,wherein the increase is probabilistic.
 17. The remote station of claim5, wherein the transmission rate is increased or decreased in responseto the received busy signal, the amount of increase or decreaseconditioned on a Quality of Service (QoS) service level.
 18. A wirelesscommunication system, comprising: a plurality of remote stations, eachof a subset of which transmit an access request message to form aplurality of access request messages; a base station for: receiving theplurality of access request messages; measuring the utilization of theshared resource; allocating a shared system resource among the pluralityof remote stations; transmitting zero or more individual access grantsto a subset of the requesting remote stations and zero or more commonaccess grants to the remaining requesting remote stations; andtransmitting a multi-valued busy signal when the measured utilizationexceeds a pre-determined threshold.
 19. The wireless communicationsystem of claim 18, wherein the requesting remote stations receive thetransmitted individual or common access grants and the busy signal andtransmit data to the base station respectively in accordance therewith,responsive to the received busy signal.
 20. The wireless communicationsystem of claim 18, wherein a subset of the plurality of remote stationstransmit data autonomously, responsive to the transmitted busy signal.21. A method of access control of a shared resource, comprising:receiving a plurality of access requests for transmission on the sharedresource from a respective plurality of remote stations; allocating aportion of the shared resource to zero or more of the requesting remotestations in response to the plurality of access requests, the allocationcomprising zero or one common access grant to a subset of the requestingremote stations; transmitting the common access grant to the remainingremote stations on one or more common grant channels; measuring theutilization of the shared resource; and transmitting a multi-valued busysignal when the measured utilization exceeds a pre-determined threshold.22. The method of claim 21, wherein: the allocation further compriseszero or more individual access grants to zero or more requesting remotestations; and further comprising transmitting the individual accessgrants to the respective remote stations on one or more individual grantchannels
 23. The method of claim 21, operable with the plurality ofremote stations equipped to transmit autonomously on the sharedresource, using a limited portion of the shared resource, without anaccess request or access grant, further comprising: computing theexpected amount of the shared resource to be consumed by the autonomoustransmissions and allocating the portion of the shared resource forindividual and common access grants in response thereto.
 24. The methodof claim 21, operable with one or more remote stations transmitting withpermission from one or more access grants, further comprising: decodingone or more received packets; determining if the one or more receivedpackets decoded without error; transmitting to the one or more remotestations an acknowledgment and grant extension (ACK-and-Continue)command, respectively, when the respective received packet decodedwithout error and the access grant for the respective remote station isto be extended; and wherein the allocation of the portion of the sharedresource is performed in accordance with individual and common grantsextended with the one or more ACK-and-Continue commands.
 25. The methodof claim 21, wherein the busy signal comprises a series of commands,each command one of a first value indicating a decrease or a secondvalue indicating an increase.
 26. The method of claim 25, wherein theseries of commands further comprise a third value indicating neither anincrease or decrease.
 27. The method of claim 21, wherein the busysignal comprises a series of commands, each command one of one or morevalues indicating respective one or more decreases, the respectivedecreases indicating different decrease amounts or one or more valuesindicating respective one or more increases, the respective increasesindicating different increase amounts.
 28. The method of claim 27,wherein the series of commands further comprise a value indicatingneither an increase or decrease.
 29. A method of transmission,comprising: receiving data for transmission; storing the data in a databuffer; generating an access request message; transmitting the accessrequest message; receiving one or more common grant channels from a basestation; decoding an access grant comprising a common grant on one ofthe one or more common grant channels; receiving a multi-valued busysignal from the base station; and transmitting a portion of data fromthe data buffer in response to a decoded access grant adapted inaccordance with the received multi-valued busy signal.
 30. The method ofclaim 29, further comprising: receiving one or more individual grantchannels; and wherein the access grant alternately comprises anindividual grant directed on one of the one or more individual grantchannels.
 31. The method of claim 29, further comprising transmitting alimited portion of the data in the data buffer autonomously,irrespective of whether an access grant has been received, responsive tothe received busy signal.
 32. The method of claim 29, furthercomprising: receiving an ACK-and-Continue command; and transmitting anadditional portion of data from the data buffer in response to apreviously decoded access grant adapted to the received busy signal. 33.The method of claim 29, further comprising transmitting a limitedportion of the data in the data buffer autonomously, subsequent to areceived ACK, responsive to the received busy signal
 34. The method ofclaim 29, further comprising: receiving a NAK command; andretransmitting the portion of data from the data buffer previouslytransmitted in response to a previously decoded access grant, responsiveto the received busy signal.
 35. The method of claim 29, wherein thetransmission rate is decreased in response to an assertion on thereceived busy signal.
 36. The method of claim 35, wherein the decreaseis deterministic.
 37. The method of claim 35, wherein the decrease isprobabilistic.
 38. The method of claim 29, wherein the transmission rateis increased in response to an assertion on the received busy signal.39. The method of claim 38, wherein the increase is deterministic. 40.The method of claim 38, wherein the increase is probabilistic.
 41. Themethod of claim 29, wherein the transmission rate is increased ordecreased in response to the received busy signal, the amount ofincrease or decrease conditioned on a Quality of Service (QoS) servicelevel.
 42. An apparatus, comprising: means for receiving a plurality ofaccess requests for transmission on the shared resource from arespective plurality of remote stations; means for allocating a portionof the shared resource to zero or more of the requesting remote stationsin response to the plurality of access requests, the allocationcomprising zero or one common access grant to a subset of the requestingremote stations; means for transmitting the common access grant to theremaining remote stations on one or more common grant channels; meansfor measuring the utilization of the shared resource; and means fortransmitting a multi-valued busy signal when the measured utilizationexceeds a pre-determined threshold.
 43. An apparatus, comprising: meansfor receiving data for transmission; means for storing the data in adata buffer; means for generating an access request message; means fortransmitting the access request message; means for receiving one or morecommon grant channels from a base station; means for decoding an accessgrant comprising a common grant on one of the one or more common grantchannels; means for receiving a multi-valued busy signal from the basestation; and means for transmitting a portion of data from the databuffer in response to a decoded access grant adapted in accordance withthe received multi-valued busy signal.
 44. A wireless communicationsystem, comprising: means for receiving a plurality of access requestsfor transmission on the shared resource from a respective plurality ofremote stations; means for allocating a portion of the shared resourceto zero or more of the requesting remote stations in response to theplurality of access requests, the allocation comprising zero or onecommon access grant to a subset of the requesting remote stations; meansfor transmitting the common access grant to the remaining remotestations on one or more common grant channels; means for measuring theutilization of the shared resource; and means for transmitting amulti-valued busy signal when the measured utilization exceeds apre-determined threshold.
 45. A wireless communication system,comprising: means for receiving data for transmission; means for storingthe data in a data buffer; means for generating an access requestmessage; means for transmitting the access request message; means forreceiving one or more common grant channels from a base station; meansfor decoding an access grant comprising a common grant on one of the oneor more common grant channels; means for receiving a multi-valued busysignal from the base station; and means for transmitting a portion ofdata from the data buffer in response to a decoded access grant adaptedin accordance with the received multi-valued busy signal.
 46. Processorreadable media operable to perform the following steps: receiving aplurality of access requests for transmission on the shared resourcefrom a respective plurality of remote stations; allocating a portion ofthe shared resource to zero or more of the requesting remote stations inresponse to the plurality of access requests, the allocation comprisingzero or one common access grant to a subset of the requesting remotestations; transmitting the common access grant to the remaining remotestations on one or more common grant channels; measuring the utilizationof the shared resource; and transmitting a multi-valued busy signal whenthe measured utilization exceeds a pre-determined threshold. 47.Processor readable media operable to perform the following steps:receiving data for transmission; storing the data in a data buffer;generating an access request message; transmitting the access requestmessage; receiving one or more common grant channels from a basestation; decoding an access grant comprising a common grant on one ofthe one or more common grant channels; receiving a multi-valued busysignal from the base station; and transmitting a portion of data fromthe data buffer in response to a decoded access grant adapted inaccordance with the received multi-valued busy signal.